Impulse generator



June 29, 1948. HopLEY 2,444,044

IMPULSE GENERATOR Filed July 17, 1942 INVENTOR; HORACE EDWARD HOPLEY o 306090l20l50|80 ATTORNEY Patented June 29, 1948 UNITED STATES PATENT OFFICE IMPULSE GENERATOR Application July 17, 1942, Serial No. 451,283 In Great Britain September 13, 1941 1 Claim. 1

The present invention relates to impulse generators suitable for use in automatic telephone exchanges and is more particularly concerned with the provision of simple and compact arrangements for furnishing impulses of different speeds and ratios.

In large automatic exchanges a considerable number of testing devices of the type usually known as routiners may be involved, and it is economically practicable to provide a common motordriven generator which is operated from the exchange battery and which is provided with a plurality of cam-operated im'pulsing contacts giving the various impulsing speeds and ratios required by the routiners.

In smaller exchanges, however, where only one or two routiners would be required the cost of providing'a standard motor-driven impulse generator for their use may be so heavy as to make the installation of routiners an uneconomic proposition though it may be highly desirable from a maintenance standpoint. One of the chief objects of the invention is accordingly to provide a simple, cheap and reliable impulse generator suitable for use in conjunction with one or more rout-iners in an automatic exchange, whereby the cost of installing routiners. and associated equipment is reduced to a figure which makes their use economically practicable in smaller exchanges than hitherto.

According to one feature of the invention an impulse generator suitable for use in a telephone exchange is arranged so that alternating current is applied to a gas discharge tube of the type which after it has struck remains conducting until the voltage applied to its anode circuit is reduced to substantially zero, the circuit of the tube including also an electromagnet which is operated from the time the applied alternating current voltage reaches the striking voltage until it is again reduced to zero and by its operation controls lmpulsing contacts.

According to another feature of the invention in an impulse generator suitable for use in a telephone exchange, an electromagnet is arranged to be energised and de-energ-ised alternately for substantially equal intervals by the application of rectified alternating current of suitable voltage to the anode circuit of a grid controlled gas discharge tube, the electromagnet being also connected in the anode circuit and controllin suit able impulsing contacts.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawing comprising Figs. 1 and 2. Fig. 1 is a circuit diagram showing how the output from a 16% cycles per second ringing current generator of the type normally provided in an automatic telephone exchange is utilised to furnish impulses of different rates and ratios suitable for operating one or more automatic routining equipments provided in the exchange. Fig. 2 is a graphical timing diagram of the various relays employed and the circuits they control and serves to enable the operations of the circuits to be better appreciated.

The impulse generator comprises essentially the gas discharge tube or gas filled relay GDT, for instance of the mercury vapour type, the anode voltage of which is supplied by the exchange ringing current generator which connects with leads Ill and I l and supplies current at a pressure of about '75 volts and a frequency of 16 cycles per second. The ringing current is applied to the full wave dry contact rectification arrangement FWR before connectionto the tube GDT, and the anode circuit of the tube also includes the high speed relay P.

When the preliminary start contacts PSI are closed,-the tube filament heating circuit is completed from the exchange battery via resistance YA, while the grid of the tube derives a potential from the potentiometer PR and thence via the high resistance YB, the grid potential being adjusted to a value such that the tube will only strike at substantially the peak value of the applied anode voltage.

Actual operation of the generator commences When the start contacts SI, S2 and S3 are closed, the former contacts connecting the rectified ringing current voltage to the tube GDT and contacts S3 preparing locking and operating circuits for the pulse counting relays A-F.

Referring now to Fig. 2, the applied ringing current voltage curve at the top is shown for convenience as a triangular shaped wave and it will be seen that a complete cycle occupies 6O milliseconds. The output from the full wave rectifier FWR is shown directly beneath, from which it will be seen that voltage peaks occur every milliseconds.

On the first peak of the applied voltage, tube GDT strikes and ionises in known manner, and thereupon remains in this condition until the an ode voltage falls to substantially-zero, after which it will not re-strike until the next peak voltage is reached. It will be seen that as a result the anode relay P will be operated as shown i the graphical diagram for the last half, i. e. 15 milliseconds of each 30 milli-second period, that is to say 33 times per second with a 1:1 make to break ratio.

For the purpose of testing the automatic exchange apparatus the routiners mainly require loop impulses with the usual make to break ratio of 1:2 and preferably at a rate of 11-12 impulses per second, i. e. at a slightly higher speed than corresponds to a correctly-adjusted subscribers dial, and other speeds and ratios may also be required. For this purpose the counting relays A-F are provided in association with relay P and function in the following manner to enable suitable impulses to be made available to the routiners.

On the first operation of relay P, relay A operates and at armature al prepares an operating circuit for relay B. On the first release of relay P, the short-circuit is removed from relay B which operates in series with relay A which holds. On the second operation of relay P, earth extends over armatures pl, 112 and b2 to operate relay C and on the second release of relay P, relay D operates in series with relay C which holds, while relays A and B are released at armature dl. On the third operation of relay P, relay E operates and on the third release of relay 1?, relay F operates in series with relay E which holds, and relays C and D are released at armature fl. On the fourth operation of relay P, relay A re-operates and on the fourth release of relay P, relay B operates in series with relay A and relays F and E are released and the cycle of operations repeats itself as long as the conditions remain the same.

From Fig. 2 it will be seen that after the first operation of relay F, this relay is operated once every 90 mini-seconds and remains operated each time for a period of 30 milli-seconds. The make contact 3 connected to circuit Y over leads l2 and 13 will therefore deliver pulses at the rate of 11 /9 per second with the standard subscribers dial make to break ratio of 1:2.

If pulses at the same rate but with a make to break ratio of 2:1 are required as in the case of impulses extending directly to switch driving magnets, these may be obtained by connecting normally made contacts of relay F in parallel with the normally open contact of relay B as shown by the armatures f2 and b3 which connect with circuit X over leads M and 15. Accordingly, since relay B is operated for 30 milliseconds in each 90 milli-second period, and relay F is restored to normal immediatel following the energization of relay B, remains unoperated for a period of 60 milli-seconds and then operates for a period of 30 milli-seconds, pulses at the rate of 11 /9 impulses per second are generated having a make to break ratio of 2: 1.

The same result could be obtained by omitting the armature b3 and employing armature f2 only to control the X circuit, or similar break armatures of relay B or relay D might be used to control the X circuit, but the use of the B relay make armature b3 in association with the F relay break armature f2 enables the Wave form of the output impulses more nearly to approach the ideal, since X circuit is closed at 173 at the same time that the circuit of relay F is opened by relay B. Similar arrangements might be applied in connection with the other pulsing out leads.

If a pulsing rate of the order of 22 impulses per second is required, that is to say with a cycle time of 45 milli-seconds, such as might be used for relay timing purposes in the routiner, the combination of armatures a2, 02 and (13 which connect with circuit Z over leads [5 and I! may be employed and it will be seen from Fig. 2 that impulses having a make to break ratio of 2:1 at a speed of approximately 22 impulses per second are produced.

Other combinations of armatures of relays A-F may also be employed to give the same or different sub-multiples of the basic pulsing rate of 33 /3 impulses per second with different make to break ratios. As an alternative a small stepby-step electro-magnetically operated switch may be employed in place of the counting relays A-F, and it may be found satisfactory to include the magnet of the switch in the anode circuit of the tube GDT thereby enabling relay P to be dispensed with. The step-by-step switch might be provided with wipers and suitably strapped banks or alternatively it could be provided with sets of contacts operated from suitably shaped cams mounted on its driving shaft.

What I claim as new and desire to secure by Letters Patent is:

An impulse generator comprising a source of alternating current, a gaseous discharge tube including a cathode, an anode, and a control electrode, adjustable means for impressing a variable biasin potential between said control electrode and cathode a quick-acting relay, means for energizing the anode-cathode path of said tube in series with said relay from said source, thereby causing at least one discharge to be initiated in said tube during each cycle of the alternating current wave when the anode-cathode potential rises to a critical value determined by the value of the biasing potential impressed on the control electrode thereof, each of the discharges being interrupted when the anode-cathode potential falls to a second critical value, said relay operated in response to each discharge of said tube. an impulsing circuit, and contacts controlled by said relay to produce periodic impulses, at a rate determined by the frequency of said source and at a break to make ratio determined by the adjustment of said first means, in said impulsing circuit.

HORACE EDWARD HOPLEY.

REFERENCES CITED The following references are of record in the file of this patent:

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